Remote leak detection of evacuated spaces has been performed previously by monitoring pressure change in the evacuated space over a period of time and noting pressure differences in discreet isolated volumes as being near a leak. The pressure change monitoring techniques previously used are limited to systems that permitted isolation of discreet volumes.
As related to the present invention, the ability to locate a leak in an evacuated system depends, in varying degrees, on three basic factors: the initiation of pressure increase due to the leakage at a point in time; the conductance within the evacuated vessel; and the amount of pressure increase due to leakage.
The first factor, the initiation of pressure increase at a point in time due to leakage, applies to systems which experience change in the leakage rate into the system. Examples of such systems include vacuum systems that experience an increase in leakage rate caused by external forces or cycling fatigue, or vacuum insulated superfluid helium systems which can have a super leak that will only pass leakage when the helium cools below the lambda transformation temperature (below 2.2K at std. pressure). Other related systems include those in which an existing leak has a significant increase in leakage rate at a point in time. One example of a system involves a vessel within a vessel. The inner vessel can be tested for leak detection and leak location by evacuating both vessels, then venting the inner vessel with dry air or nitrogen. During this venting, any leaks in the inner vessel wall will result in a pressure rise in the space between the vessels.
Another example is a single wall vacuum system which may be monitored by applying a volatile liquid to the outside of the system. The volatile liquid will vaporize when drawn through the leak, and cause a rise in the pressure within the vacuum system. This rise in pressure will indicate the presence of leakage and the invention provides an economical means of locating the leak.
The second factor of leak detection for the present invention involves the conductance within the vacuum system under examination. The more uniform the conductance within a space, the easier leak location application becomes. Also, the lower the conductance within the system, the easier it becomes to perform leak location and the more precise the leak location capability.
The third factor is the amount of pressure increase in the vacuum system due to the leakage from a leak. The change in pressure that occurs when the leak comes into existence or increases in leakage rate must be significant enough to be measured by the pressure gauges. The total volume of the vacuum system, its conductance, system pumping speed (if any), pressure, leakage and outgassing rates will determine the minimum detectable leakage rate.
Helium mass spectrometer leak testing can be more sensitive than the present invention, but it requires a greater degree of human access when used for leak location, and it is more time consuming and expensive when used for leak location on large systems.
Pressure change measurement is remote and is as sensitive as the invention, but it is limited in application to systems that can be isolated in discreet volumes. Further, it is not capable of as precise a location function as the present invention.